I'm thinking I'll probably want to float the floor, but maybe not the walls and ceiling. I want isolation and a great sounding room, but not for more than $25,000 or so. I can't even justify more than that to myself, let alone my wife (haha)!
barthowk,
Floating the floor but not the walls and ceiling is practically useless...The idea of "floating" is to separate each structural element from the ones adjoining it...This is to diminish (or practically eliminate) any structural vibrations being transferred from one room to another...The simple analogy is that floating is used to keep outside sounds (vibrations) from coming in, and inside sounds (vibrations) from going out...
Another critical element to this factor is HVAC ductwork...If your control room and your studio area (iso booths, etc.,) are serviced by connected ducts, you will never achieve total isolation...Remember, audio waves are vibrations of the airspace within your listening area and, if you have open vents in your control room that are connected to open vents in your studio, it doesn't take a rocket scientist to figure out what the results will be...
I'm inclined to agree with Noah 330 (if you have the property footage needed)...You'd be much better off building a free-standing structure behind the garage...There are, however, a few things to consider...probably your main concern will be how this additional structure could affect future resale value (and, perhaps your property taxes)...
The bathroom issue presents a different set of problems...Running water & flushing toilets produce a lot of noise...Water pipes are notoriously noisy...You also need to consider the (hopefully, unlikely) event that a water pipe could burst and wreak havoc on your studio...
This can be, somewhat, circumvented by having the physical location of the bathroom situated somewhere near the rear of the control room part of your structure (in an exterior area so that you don't have any water pipes situated in acoustically sensitive interior areas)...
Here's an section from a design for a home/residential studio that I've been working on that my wife and I are planning to build in the near future...
Note that there is complete separation from the control room, yet there is still easy access to the bathroom from the control room...The fixtures that require water are all located on an exterior wall, meaning the water supply never has to be fed through ceilings or interior walls (what isn't shown in this sectional is that the hot water heater is located in the garage's utility room which is less than 30' away from the bathroom)...
You can build a nice and very functional structure with a $25K budget, but it's probably not going to be nearly as large (or as acoustically "isolated") as you think it will be unless you do a lot of the finishing work and manual labor yourself (or, you can have a "barn-raising" weekend and invite friends who know how to do this kinda stuff)...
Good luck on this project! Do it right and you'll get years of enjoyment from it!